This invention relates to an improvement in the cooling performance of an electric generator for use with vehicles and, more specifically, to the simplification of such structure by separating a cooling fan from the rotor of the generator. In general, in generators for use with vehicles, since the rotor is driven from the engine or the like and a cooling fan for the generator is secured to the rotor, the cooling fan rotates at the same speed at the rotor. Accordingly, it is required to restrict the power of the engine at a low speed area, since the cooling air is insufficient in this area. Further, since the fan is secured to the rotor, there is a restriction in the locating of components such as the rectifier and voltage regulator.
FIG. 1 shows a conventional embodiment of an AC generator for use with vehicles, in which are shown a rotor 1, field coils 1a, a rotary shaft 11 for the rotor, a stator 2 disposed opposed to the rotor by a slight radial gap and having armature coils 2a in which a three phase AC output is induced, bearings 31, 32 provided on either side for rotatably supporting the rotary shaft 11, brackets 41, 42 disposed on either side, respectively, a pulley 5 mounted at the end of the shaft 11, a cooling fan 6 secured to the end of the shaft 11 opposite the pulley, a cup-shaped cover 7 mounted to the bracket 42 and having a vent hole 71, a rectifier 91 for rectifying the three phase AC output and a voltage regulator 92 for regulating the three phase AC output. The position and mounting of the rectifier 91 and the voltage regulator 92 will, as known to those skilled in the art, vary in accordance with the component dimensions and the available mounting space.
The operation of the conventional apparatus will now be explained. The rotor 1 is driven by way of the pulley 5 from an engine or the like (not shown), by which three phase AC power is generated from the stator 2. Since the rotor 1 and the stator 2 generate heat due to ohmic losses, the cooling fan 6 secured to the rotor 1 supplies cooling air for carrying off the heat. The passage of the cooling air is as shown by arrows. Since the amount of cooling air is in proportion to the rotational speed of the cooling fan 6, a sufficient amount of cooling air cannot be supplied at low speed operation of the generator. Further, as can be seen from FIG. 1, available mounting locations for the rectifier 91 and voltage regulator 92 are limited for it is necessary to arrange the rectifier 91 and the voltage regulator 92 so as to not be in contact with the shaft 11 of the rotor securing the fan 6. This causes a restriction in the utilization of space. FIG. 2 schematically shows the restricted area, in which the hatched area is a utilizable range.